Segmentation in Operating System (OS)

Segmentation in Operating system (OS) is a memory management technique and it follows the non-contiguous memory allocation method.

Segmentation meaning and Definition:

Segment is defined as “it is a logical grouping of instruction such as subroutine, array or data area which are not necessarily all of the same sizes are called segments.”

Every program (job/process) is a collection of these segments and each segment is not an equal size (not fixed partition).

The process is divided into modules (segments) for better visualization.

Segmentation is a technique for managing these segments.

Why Segmentation is required?

Segmentation divides the process into the segments.

Each segment contain same type of functions such as main function can be included in one segment and the library functions can be included in the other segment. So segmentation is used to improve efficiency of the system.

Segment Table:

The OS search the entire main memory for free space to load a segment. This mapping done by segment table.

The details about each segment are stored in a table called as segment table. Segment table is stored in one (or many) of the segments.

Each entry of the segment table includes ‘Segment Number’, ‘Segment Base’ and  ‘Segment Limit’

Segment Base: Contains the starting physical address where the segment resides in memory.

Segment Limit: Specifies the limit of the segment.

Click here for Segmentation Structure

Address generated by CPU (Logical Address) is divided into two parts:

I] Segment Number (S):

It is used as an index into the segment table. Number of bits required to represent the segment.

II] Segment Offset (D):

Number of bits required to represent the size of the segment.

Consider following illustration to understand above:

Segment Number Limit Base
0 800 2000
1 400 2500
2 1200 1500
3 1500 5000


Segment Number – Indicates Segment

Limit – Indicates length or size of segment

Base – Indicates starting address of the segment in main memory

So loading size range in the main memory from base to limit is considered as segment loaded range.

Storage of segment in main memory is indicates as:  

For segment ‘0’ = Limit + Base = 2800

For segment ‘1’ = Limit + Base = 2900

For segment ‘2’ = Limit + Base = 3700

For segment ‘3’ = Limit + Base = 6500

Main Memory representation is as:

Segment – 0


Segment – 1

Segment – 3

Segment – 2



Advantages of Segmentation:

1] Allows dynamically growing

2] It allows to divide the program into modules which provides better visualization

3] Segment table consumes less space as compared to Page Table in paging

4] It solves the problem of internal fragmentation

5] It support virtual memory

Disadvantages of Segmentation:

1] There is an overhead of maintaining a segment table for each process.

2] The time taken to fetch the instruction is large

3] Segments of unequal size are not suited for swapping

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Deadlock in OS

Deadlock meaning in OS:

The main reason is to occur deadlock in OS is, in multi-programming environment several processes request the resources from OS. If the resources are available at that time, then OS permits the resources to that process, if not available then process has to wait until resources are released. Because not releasing the resources are blocked by others. This situation is said to be deadlock

Deadlock Definition:

According to P. B. Prasad, “A process request” the resources, the resources are not available at that time, so the process enters into the waiting state. The requesting resources are held by another waiting process, both processes are in waiting state, this situation is called as deadlock”.

Deadlocks are a set of blocked processes each holding a resource and waiting to acquire a resource held by another process.

Example of Deadlock:

P1 and P2 are two processes

R1 and R2 are two resources

P1 request the resources R1 which is already held by process P2.

P2 request the resources R2 which is already held by process P1.

Then both process enters in to the waiting state. There is no work progress or release of resources which leads to deadlock situation.

Deadlock Resource Allocation Graph:

Deadlock can be represented by resource allocation graph.

It is also called as deadlock diagram

Here, Process represented by circle

Resources represented by square

Edges represented for requesting and assigning

Deadlock Conditions in OS:

A deadlock system must satisfy the following 4 conditions. Conditions for deadlock are as:
1] Mutual Exclusion

2] Hold and Wait

3] No preemption

4] Circular wait

1] Mutual Exclusion:

Mutual exclusion means resources are (at least one) in non-sharable mode only.

It means only one process at a time can use a resource.

2] Hold and Wait:

Each process in the deadlock state must hold at least one resource and is waiting for additional resource that are currently being held by other processes.

3] No preemption:

Resources are not released in the middle of the work, they released only after the process has completed its task.

4] Circular wait:

All the processes must wait for the resource in a cyclic manner where the last process waits for the resource held by the first process.

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Round Robin Scheduling Algorithm

Round Robin Scheduling Algorithm is a CPU scheduling in OS is a preemptive scheduling in which each process gets executed in a cyclic way. It means that particular time slice is allotted to each process which is known as time quantum. This post focus on Round Robin Scheduling Algorithm with example, advantage and disadvantage

CPU is assigned to the process on the basis of FCFS for a fixed amount of time which is called quantum (Cyclic nature).

Once an assigned process is executed for given time period that process is preempted and other ready process executes for given time period.

If the execution of the process gets completed in that time quantum, then the process will get terminate otherwise the process will again go to the ready queue, and the previous process will wait for the turn to complete its execution.

Context switching is used to save states of preempted processes.

This cyclic context switching called as Round Robin scheduling because of each process takes equal time and handover to other and waiting for next round.

It generally used by those operating system which has multiple clients to make use of resources.

Example of Round Robin Scheduling:

Advantage of Round Robin Scheduling:

1] Gives the best performance in terms of average response time.

2] It is best suited for time sharing system

Disadvantage of Round Robin Scheduling:

1] It leads to starvation for processes with larger burst time as they have to

repeat the cycle many times.

2] Its performance heavily depends on time quantum.

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Priority Scheduling Algorithm

Priority Scheduling means allocating the CPU first to those processes has higher priority. Priority scheduling is one of the most common scheduling algorithms in batch systems. These post focus on priority scheduling algorithm.

Each process is assigned a priority. Process with the highest priority is to be executed first and so on.

A priority is a number in a range (for instance between 0 to 255) which is predefined by operating system.

A small number would mean high priority while a large number would mean low priority (It a as per LINUX system. It may vary to other system like large number would mean low priority while small number would mean high priority)

Scheduling policy pick the processes in the ready queue having the highest priority.

Processes with same priority are executed in First-Cum-First-Serve(FCFS) manner.

Priority can be decided based on memory requirements, time requirements or any other resource requirement.


Process Burst Time Priority
P1 7 3
P2 23 2
P3 12 1
P4 5 4

Gantt represents the priority scheduling algorithm as:

As per LINUX Nomenclature:

P3 P2 P1 P4

0                            12                             35                             42                     47

Because of high priority of P3 it start executing, so waiting time is ‘0’ millisecond and others process is in waiting state. P2 waits for ’12’ millisecond, P1 waits for ’35’ millisecond, P4 waits for ’42’ millisecond.

P3 completion time is ’12’ millisecond, completion time is ’35’ millisecond, P1 completion time is ’42’ millisecond and P4 completion time is ’47’ millisecond.

The average waiting time as per the above represented Gantt chart (priority scheduling algorithm) is:

Average waiting time = 0 + 12 + 35 + 42 / 4

                                         = 89/4

                                         = 22.25 millisecond

Advantage of priority scheduling algorithm:

Mechanism to provide relative importance to processes

Disadvantage of priority scheduling algorithm:

Could lead starvation of low priority process

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XAT 2020 Exam Date, Eligibility, Registration, Application Fee, Syllabus

XAT 2020 entrance exam will be conducted on Sunday, 5th January, 2020. XLRI conducts XAT on behalf of XAMI. Registration for XAT 2020 and appearing for XAT 2020 is the preliminary step towards applying to XLRI and XAT Associate Institutes. These articles focus on XAT 2020 Exam Date, Eligibility, Registration, Application Fees, Syllabus and list of exam cities where XAT 2020 conduct.

XAT 2020 Registration as a new condidate.

XLRI is conducting XAT at all India level to select the most appropriate students for management education. The XAT score is being used by more than 150 institutes for the admission.

XAT 2020 Exam Important Dates:

XLRI has announced the XAT exam date 2020 and other important dates for XAT 2020 exam as under:

Activity Dates
Registration Start Date: 23rd August 2019
Registration Last Date: 4th week of November  2019
Releasing of admit card: 20th December 2019
XAT 2020 exam date 5th January 2020
Declaration XAT 2020 Result 31st January 2020
Mode of Exam: Online

Application Fees:

XAT Registration Fee (without late fee) : Rs. 1700/-
XAT Registration Fee (with late fee) : Rs. 2000/-

XAT 2020 Eligibility Criteria:

As per the XAT 2020 eligibility criteria, one must have a bachelor’s degree in any discipline from a recognized board or university. The duration of the graduation should be a minimum of three years.

Final year graduation students can also apply for the same

XAT 2020 Syllabus (Exam Pattern):

Verbal and logical ability
Decision making
Quantitative ability and data interpretation
General knowledge

Total Questions : 99

Total Marks: 99

Mode of Exam: Online

Negative Marking: Yes

 XAT 2020 Association Institutes Where XAT 2020 Score Applicable click here

XAT 2020 will be conducted in following cities:

Agra, Ahmedabad, Allahabad, Ambala, Amravati, Amritsar, Bengaluru, Berhampur, Bhatinda, Bhilai Nagar, Bhopal, Bhubaneswar, Bokaro Steel City, Chandigarh/Mohali, Chennai, Coimbatore, Cuttack, Dehradun, Delhi-NCR, Dhanbad, Dibrugarh, Durgapur/Asansol, Ernakulam, Gandhinagar, Goa, Gorakhpur, Guwahati, Gwalior, Hooghly, Hubballi(Hubli), Hyderabad, Indore, Jabalpur, Jaipur, Jammu, Jamshedpur, Kannur, Kanpur, Kolkata, Kota, Kottayam, Kurnool, Kurukshetra, Lucknow, Ludhiana, Madurai, Mangalore, Mumbai, Mysuru(Mysore), Nagpur, Nashik, Patna, Pune, Raipur, Rajahmundry, Ranchi, Roorkee, Rourkela, Sambalpur, Siliguri, Surat, Thiruvananthapuram Tiruchirappalli, Tirupathi, Tiruvallur, Udaipur, Udupi Vadodara, Varanasi, Vijayawada, Visakhapatnam, Warangal.


XLRI reserves the right to change or cancel any Test City/Centre.

Click here for more official details




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NMAT 2019 Exam Date, Registration, Application Fees

NMAT exam is conducted by GMAC. Those who want to pursue MBA or other graduate management program from leading management institute in India then NMAT 2019 is the best choice to appear. These articles focus on NMAT 2019 Exam Date, Registration, and Application Fees.

NMAT 2019 Important Dates:

Following are the important date of NMAT 2019:

Activity Start Date End Date
Registration  Tuesday, July 02, 2019

Thursday, October 03, 2019
Late Registration  Friday, October 04, 2019

Monday, October 14, 2019
Registration – Retake  Saturday, October 05, 2019

Saturday, December 14, 2019
Re-scheduling  Tuesday, July 02, 2019  Saturday, December 14, 2019
Re-take Scheduling  Saturday, October 05, 2019  Saturday, December 14, 2019
Exam Delivery  Friday, October 04, 2019  Tuesday, December 17, 2019
Final Announcement of Results 3rd week of January, 2020
Official Scorecard Download Tuesday, March 31, 2020

NMAT 2019 Application Fees:

As per the activity below are the fees declared by NAMT 2019 exam:

Test Registration (Early): INR 2000 + applicable taxes
Test Registration (Late) : INR 2500 + applicable taxes
Retake : INR 2000 + applicable taxes
Reschedule: INR 1100 + applicable taxes
Additional Score Reports (beyond first five) : INR 200 per Score Report + applicable taxes

NMAT 2019 Payment Mode:

Following are the mode of payment accepted by NMAT 2019:

1) Visa
2) MasterCard
3) American Express
4) Debit Card
5) Net Banking
6) Diners Club
7) Mobile Wallets

Accepted as an admissions criterion by the leading management institutions in India:

Today the NMAT by GMAC is accepted by the following leading institutions and this list is growing. Pursuing a management degree at one of these universities makes the pursuit of your dreams that much easier.

1) Bengaluru, Karnataka
2) Jain University – CMS Business School
3) Amrut Mody School of Management, Ahmedabad University, Ahmedabad
4) BSE Institute Limite, Mumbai
5) Amity University, Delhi NCR
6) SRM University, Chennai, Delhi NCR Sonipat
7) University of Petroleum & Energy Studies (UPES), Dehradun
8) BML Munjal University, Delhi
9) VIT University, Vellore
10) ITM Business School, Navi Mumbai
11) Mody University, Rajasthan
12) GITAM School of International Business, Visakhapatnam
13) Hyderabad Business School, GITAM University, Hyderabad
14) Jindal Global Business school – Delhi/NCR

Test Cities:

There are number of test centres declared by NMAT 2019 in various city in National and International level which are:

National Level:

Cities Region
Agra, Chandigarh, Dehradun, Delhi, Faridabad, Gurgaon, Jammu, Kanpur, Lucknow, Noida, Patiala, Varanasi North
Aurangabad, Rajkot, Ahmedabad, Jaipur, Jodhpur, Kota, Mumbai, Nagpur, Nasik, Pune, Pilani, Surat, Vadodara West
Bengaluru, Chennai, Kochi, Hyderabad, Manipal, Mysore, Tiruchirapalli, Vellore, Vizag, Vijaywada Sauth
Bhopal, Indore, Jabalpur, Raipur Central
Bhubaneswar, Guwahati, Jamshedpur, Kolkata, Patna, Ranchi, Shillong East

International Level:

Location Country
Kathmandu Nepal
Thimphu Bhutan
Dhaka Bangladesh
Colombo Srilanka




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CAT 2019 Exam Date, Registration

Common Admission Test (CAT) 2019 exam will be held on Sunday, 24th November, 2019 in morning and evening session and registration started from 7th August, 2019. Indian Institute of Management (IIM) conduct CAT exam every year for various post graduate programs. This article focused on CAT 2019 Exam Date, Registration date which is declared by IIM’s.

CAT exam is a National level exam. On the basis of CAT 2019 score aspirant can also get admission into other management

CAT 2019 Exam Date, Registration:

Following are the important dates for the registration and exam. Click here for official date or update of CAT 2019 exam:

Event Important Date
Exam Date Notification: 28th July, 2019
Online Registration Start: 7th August, 2019
Last Date of Registration:  18th September, 2019
Admit card download: 23rd October, 2019
Test date: 24th November, 2019
Result declaration: Second week of January, 2020

Click here for CAT 2019 Registration
CAT 2019 will be conducted by IIMs as a pre-requisite for admission to various management programmes of IIMs.

These programmes are like MBA, PGP, PGPEM, PGPPM, PGPBA etc.

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History of Operating System (OS)

Probably many of us don’t have idea about what is operating system, history of operating system (OS) and how operating system works. Computer system, mobile device and other electronica devices has operating system which plays important role to perform different operations.

An operating system is the most important programs or operations or tasks that runs on a computer.

It perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of all files and directories on the disk, memory management and controlling peripheral devices such as disk drives and printers.

Operating systems can be found on a countless number of items including:

  1. Mobile phone
  2. ATM machines and
  3. Even many modern day automobiles
When and why we started to use operating system. The detailed history of Operating system is as:

The First Generation (1940 to early 1950):

When electronic computers where first introduced in the 1940’s they were created without any operating systems.

All programming was done in absolute machine language, often by wiring up plug boards to control the machine’s basic functions.

During this generation computers were generally used to solve simple math calculations, operating systems were not necessarily needed.

The Second Generation (1955 to 1965):

The first operating system was introduced in the early 1950’s, it was called GMOS and was created by General Motors for IBM’s machine the 701.

Operating systems in the 1950’s were called single-stream batch processing systems because the data was submitted in groups.

These new machines were called mainframes, and they were used by professional operators in large computer rooms.

The Third Generation (1965 to 1980):

By the late 1960’s operating systems designers were able to develop the system of multiprogramming in which a computer program will be able to perform multiple jobs at the same time.

Multiprogramming system allowed a CPU to be busy nearly 100 percent of the time that it was in operation.

Helps to phenomenal growth of minicomputers development and started towards personal computer.

The Fourth Generation (1980 to Present Day):

The fourth generation of operating systems saw the creation of personal computing.

One of the major factors in the creation of personal computing was the birth of Microsoft and the Windows operating system.

The windows Operating System was created in 1975 with a vision to take personal computing to the next level.

MS-DOS in 1981. Some other operating system also developed after some modification in functions like

Windows 95

Windows 98

Windows XP etc.

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Functions of Operating System (OS)

As a core system software program, basic functions of operating system plays important role to run various application on the hardware and makes it usable for the user to interact with the system so that they can send command through input and receive result as a output. This article focus on how execute command successfully using basic characteristics, functions of operating system and role of operating system function.

Following components of operating system serves basic functions of OS to perform all the basic tasks of computer and acts as communication bridge (interface) between user and computer system.

I] Interface user and resources

II] Coordination between hardware resources

III] Memory Management

IV] Processor Management

V] Device Management

VI] File Management

VII] Security

VIII] Controlling

XI] Error Detecting

X] Job Accounting

I] Interface user and resources:

Operating System (OS) provides an interface between user and computer system through Graphical User Interface (GUI) or Command Line Interface (CLI)

II] Coordination between hardware resources:

An OS enables coordination of hardware components to make communication successful between software and hardware

III] Memory Management:

The OS allocates, de-allocates and manages the primary memory or main memory as per process request.

IV] Processor Management:

An OS decides the order in which processes have access to the processor, and how much processing time each process has. It is also called as process scheduling.

V] Device Management:

An Os manages all device communication via their respective drivers and keep tracks of all device connected to the system

VI] File Management:

An Operating System does the various activities for file management via file system and directories

VII] Security:

It helps to prevents unauthorized access to programs and user data.

VIII] Controlling:

Control and monitor over system health and performance

XI] Error Detecting:

An OS constantly monitors the system to detect errors and avoid the malfunctioning of computer system

X] Job Accounting:

Keeping track of time and resources used by various jobs and users

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